1. Field of the Invention
The present invention is directed to a chopping energization control device including a switching element interposed between one end of a load and one terminal of a power supply and another switching element interposed between the other end of the load and the other terminal and energizing the on chopping mode in such a manner that both the switching elements are turned on and off load in synchronization and such operations are repeated. This chopping energization device is used, for example, to energize each of plural phase coils of a SR motor (Switched Reluctance Motor)
2. Prior Art
For example, in a device for energizing an SR motor or an SR driver for switching plural (for example, 3) phases or alternating energization and deenergization of the phase coil of each of the plural phases in order to operate the SR motor, a pair of switching elements are provided at opposite ends of the phase coil and the upper side switching element or both of the switching elements are turned on and off in intermittent fashion (chopping operation). In addition, for delivering a predetermined output torque from the SR motor, an amount of target current is passed through the phase coil in such a manner that the amount is regulated to be constant by turning on and off the switching elements in alternate fashion. Conventionally, when the switching element, which is in the form of an insulated gate bipolar transistor, is brought into chopping mode operation, the resultant electric power loss of the switching element has been at issue due to the fact that such the loss is turned into heat which will bring thermal breakdown of the module. In order to prevent such a drawback, the inventor has proposed a device for the prevention of overheating in Japanese Patent Laid-open Print No. Hei. 10-337084 which operates in such a manner that the temperature of the switching module is measured, the temperature changing speed is calculated which corresponds to the amount of current passed in the phase coil, based on these variables the instant temperature in the switching module is estimated, and if the instant current is found to be higher the current passed through the phase coil is restricted. On the other hand, as to bow to maintain the target amount of current at a constant value, the inventor provides three methods in Japanese Patent Laid-open Print No. Hei. 8-172793. One of the methods, so-call soft chopping method, is to turn on and off one of the switching elements in alternate fashion which are associated with the phase coil. The second method, so-called hard chopping, is to turn on and off alternately one of the switching elements in synchronization with alternate turning on and off the other. The third method is a combination of the soft chopping method and the hard chopping method which is established depending on the driving condition of the SR motor.
However, when the hard chopping method is employed, due to the fact that one of the switching elements differs inevitably from the other in switching characteristics, even though both the switching elements are driven by a common signal, simultaneous same switching actions of the switching elements are not always established. Thus, due to the resulting timing error, an electric power loss or chopping loss is concentrated in either of the switching elements.